Android need help with nine-patch tool to stretch image horizontally

Can someone explain to me how to prepare a PNG image as a nine-patch for Android? I don't believe that the Android link (http://developer.android.com/guide/developing/tools/draw9patch.html) is helpful enough. Here is my image that I want to stretch horizontally:

When I add the image to the nine-patch tool, there is really no option for me to draw any black lines. So then I added blank pixels around the image, and added black lines, which generated the following nine-patch:

If somebody could explain to me, or perhaps show me how to prep开发者_如何学Care my PNG to stretch horizontally, I'd really appreciate it...